About Arlington's Automatic Counters

Arlington County maintains a system of continuous automatic counters to detect and record bicycle and pedestrian volumes 24 hours a day at selected locations. Collecting better active transportation data is essential to building long-term support for walking and cycling, and for improving conditions for those who choose to walk and ride bikes. The County currently has 32 permanent installations, and six portable counters to gauge and monitor usage and demand.

The Bicycle & Pedestrian Counter Dashboard on BikeArlington.com was developed to display data from the counters, and to allow the public to consult, download, improve, and analyze it. The dashboard shows the total number of bicyclists and/or pedestrians counted at each location during the time period chosen by the dashboard user. It allows for using a number of “filtering” parameters, such as mode (bicycle and/or pedestrian), direction, and day(s) of the week. The count data from each device can be graphed within the Dashboard application, or exported to an Excel spreadsheet. The Dashboard is a work in progress, and we welcome the public’s help in improving it. The counters generate “planning level” data. That means that results are correct to much better than “order of magnitude” level, and that they are the best available. No claim is made that the data is “accurate”, “precise”, or “true”. (For a brief introduction to these concepts see Wikipedia.)

Factors That Can Affect Count Accuracy

Reliable active transportation data is still a recent innovation, and Arlington is a trend-setter in the field. We recognize that the count results are subject to a number of factors that can affect accuracy, and that some user queries might return “No Data.” The reasons for this include, but are not limited to: the particular technologies employed; the age and generation of the devices themselves; and extrinsic factors such as damage, interference by insects (!), extreme weather, and vandalism. We work diligently to limit sources of machine downtime, and systematic and random error.

Limitation Due to Type of Device

Arlington's automatic counters come in several varieties. Most of the devices installed on shared-use trails distinguish between bicycles and pedestrians, generate discrete totals for the two modes, and detect direction of travel. Other counters, such as those in on-street bike lanes, only count bicycles, and assume a single direction of travel. If your query asks for direction of travel, but the counter does not have that capability, the search will return "No Data." Similarly, if your query asks for only bicyclists or pedestrians, and the counter you select does not distinguish between the modes, the search will return "No Data." Almost all of our counting instruments come from the firm Eco-Counter.

Machine Installation Dates

Arlington's automatic counters have been installed over more than five years. If the time period of your query includes dates before a particular counter was installed, any results will not include bicycle or pedestrian activity prior to installation.

Machine Downtime

Counters occasionally go offline for a variety of reasons, including routine maintenance, insect infestation, or damage. If a counter was offline for any reason during the selected time period, the results of your query cannot include bicyclists and pedestrians who passed the counter location during the downtime. Over time, we hope to develop normalized data “patches” to fill such gaps, and will flag them.

Arlington County Commuter Services (ACCS) is funded in part by grants from the U.S. Department of Transportation (DOT), the Virginia Department of Transportation (VDOT) and the Virginia
Department of Rail and Public Transportation (DRPT).